X射线暗弱孤立中子星RX J0720.4-3125中磁场快速衰减的迹象
Indication of rapid magnetic field decay in X-ray Dim Isolated Neutron Star RX J0720.4-3125
AI总结：
本文利用孤立中子星RX J0720.4-3125的X射线光度、自转周期二阶导数和磁场独立测量，证明其自转周期导数演化与偶极场磁能耗散速率一致，揭示磁场衰减时标约为一万年。
摘要：
中子星的磁场演化是一个长期存在的争论。对于孤立的、无吸积的中子星，磁场衰减速率可以通过测量自转周期的负二阶导数来量化。或者，该速率可以通过观测相对于标准冷却（不涉及额外加热机制）的热辐射超出量来估计。附近的一颗冷却孤立中子星——RX J0720.4-3125——为探测磁场衰减提供了独特的机会，因为对该源有表面X射线光度、自转周期二阶导数和磁场的独立测量。我们证明，如果释放能量的显著部分以X射线形式发射，则自转周期导数的演化速率与偶极场磁能耗散速率相对应。磁场衰减的瞬时时间尺度约为$10^4$年。
英文摘要：
Magnetic field evolution of neutron stars is a long-standing debate. The rate of magnetic field decay for isolated, non-accreting neutron stars can be quantified by measuring the negative second derivative of the spin period. Alternatively, this rate can be estimated by observing an excess of thermal emission with respect to the standard cooling without additional heating mechanisms involved. One of the nearby cooling isolated neutron stars -- RX J0720.4-3125, -- offers a unique opportunity to probe the field decay as for this source there are independent measurements of the surface X-ray luminosity, the second spin period derivative, and magnetic field. We demonstrate that the evolution rate of the spin period derivative is in correspondence with the rate of dissipation of magnetic energy of the dipolar field if a significant part of the released energy is emitted in X-rays. The instantaneous time scale for the magnetic field decay is $\sim 10^4$ years.
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